模拟其静态初始值设定项引发ExceptionInInitializerError的类

Question

我有一个场景，我需要从未知来源加载类并实例化它们以进行模拟——我不需要运行代码，但方法和属性必须在结果实例中。我还需要类的名称保持不变，以便将其实例分配给其他已加载类的该类型的字段。有时类实例化由于ExceptionInLaunalizerError而失败，使类处于无效状态，无法恢复。我不知道哪个类会事先失败。

考虑一下这一点：

class A {
    static {
        // Throws exception, resulting in 'A' changing to an error state
    }
}
    
class B {
    // In case 'A' could not be instantiated properly, I wish to mock
    // it so it can be assigned to this field
    private A someField;
}

以下是我想到的：

1. 使用ByteBuddy-fails with NoClassDefFoundError创建失败类的子类，这可能是因为超类处于错误状态

我错过什么了吗？有没有更简单的方法来实现我的目标？

我最终找到了某种可行的解决方案，但我无法让Byte Buddy在没有静态初始值设定项的情况下过滤出类（它将计算每个类的帧）

agentBuilder = agentBuilder.type(ElementMatchers.any())
    .transform((builder, type, classLoader, module) -> builder
        .visit(new AsmVisitorWrapper.AbstractBase() {
            @Override
            public int mergeWriter(int flags) {
                return flags | ClassWriter.COMPUTE_FRAMES;
            }

            @Override
            public ClassVisitor wrap(TypeDescription instrumentedType, ClassVisitor classVisitor,
                                     Implementation.Context implementationContext, TypePool typePool,
                                     FieldList<FieldDescription.InDefinedShape> fields,
                                     MethodList<?> methods, int writerFlags, int readerFlags) {
                if (methods.stream().noneMatch(MethodDescription::isTypeInitializer)) {
                    return classVisitor;
                }
                return new ClassVisitor(Opcodes.ASM9, classVisitor) {
                    @Override
                    public MethodVisitor visitMethod(int access, String name, String descriptor,
                                                     String signature, String[] exceptions) {
                        MethodVisitor methodVisitor = super.visitMethod(access, name, descriptor,
                                signature, exceptions);

                        methodVisitor = new JSRInlinerAdapter(methodVisitor, access,
                                name, descriptor,
                                signature, exceptions);

                        if (name.equals("<clinit>")) {
                            methodVisitor = new TryCatchBlockSorter(methodVisitor, access, name,
                                    descriptor, signature, exceptions);

                            methodVisitor = new MethodVisitor(Opcodes.ASM7, methodVisitor) {
                                private final Label start = new Label();
                                private final Label end = new Label();
                                private final Label handler = new Label();

                                @Override
                                public void visitCode() {
                                    super.visitCode();
                                    visitTryCatchBlock(start,
                                            end,
                                            handler,
                                            "java/lang/RuntimeException");
                                    visitLabel(start);
                                }

                                @Override
                                public void visitMaxs(int maxStack, int maxLocals) {
                                    visitJumpInsn(Opcodes.GOTO, end);
                                    visitLabel(handler);
                                    visitInsn(Opcodes.RETURN);
                                    visitLabel(end);
                                    super.visitMaxs(maxStack, maxLocals);
                                }
                            };
                        }
                        return methodVisitor;
                    }
                };
            }
        }));

此外，我在某些类上遇到以下异常，可能是Byte Buddy错误？

[Byte Buddy] ERROR ch.qos.logback.core.util.COWArrayList [ClassLoader@3b00856b, unnamed module @4189d70b, loaded=false]
java.lang.NullPointerException
    at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$Reducing.onGenericArray(TypeDescription.java:2326)
    at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$Reducing.onGenericArray(TypeDescription.java:2281)
    at net.bytebuddy.description.type.TypeDescription$Generic$OfGenericArray.accept(TypeDescription.java:4415)
    at net.bytebuddy.description.method.MethodDescription$Token.asSignatureToken(MethodDescription.java:1915)
    at net.bytebuddy.description.method.MethodList$AbstractBase.asSignatureTokenList(MethodList.java:109)
    at net.bytebuddy.dynamic.scaffold.inline.RebaseDynamicTypeBuilder.make(RebaseDynamicTypeBuilder.java:227)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.doTransform(AgentBuilder.java:10438)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10374)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.access$1600(AgentBuilder.java:10140)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$Java9CapableVmDispatcher.run(AgentBuilder.java:10833)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$Java9CapableVmDispatcher.run(AgentBuilder.java:10771)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10330)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$ByteBuddy$ModuleSupport.transform(Unknown Source)
    at java.instrument/sun.instrument.TransformerManager.transform(TransformerManager.java:188)
    at java.instrument/sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:563)

Answer 1

如果一个类未能加载，它将永远被破坏。您所能做的是，在加载类之前，通过操纵它们的字节码来插入这些类。例如，可以使用Byte-Buddy重新定义类，以完全删除静态初始值设定项。如果使用Mockito另外模拟这些类，那么如果选择模拟它们，它们将无法执行任何代码。

您可以通过添加Java代理或实现自定义的类加载器（在定义之前显式转换任何类）来插入类。